Air France put the total cost of last month's two-week pilots strike at 500 million euros ($632 million) on Wednesday, wiping more than a fifth off its parent group's estimated full-year core profit.
Air France-KLM, Europe's second-biggest network carrier by revenue, had already revised down its target for 2014 earnings before interest, tax, depreciation and amortization in July from 2.5 billion euros to between 2.2 and 2.3 billion.
At the time, it mainly cited overcapacity on long-haul routes and weak cargo demand. The strike has added to its woes.
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Air France-KLM said total passenger traffic fell 15.9 percent in September, adding that bookings for the fourth quarter were down by between 1 and 2 percentage points.
The company said the 500 million euro cost estimate included a 320-350 million euro direct impact that took account of lower receipts and the purchase of tickets for customers on rival airlines, with costs partly offset by savings on fuel and other costs. The remainder was down to the delay in bookings.
Chief Financial Officer Pierre-Francois Riolacci told reporters the airline had sold some 28 percent of capacity for the fourth quarter, compared with 30 percent normally at this stage of the year.
"The group estimates that part of this delay could be progressively reduced over the coming weeks," the carrier said in a statement, adding that it was difficult to "quantify this adjustment exactly given the exceptional nature of the event".
Pilots ended the airline's longest strike since 1998 in late September after managers agreed to drop plans to set up a new European arm for low-cost unit Transavia. Air France plans to press ahead with the expansion of Transavia France.